#15696: Derived Ord instance for enumerations with more than 8 elements seems to be incorrect -------------------------------------+------------------------------------- Reporter: mrkkrp | Owner: osa1 Type: bug | Status: patch Priority: highest | Milestone: 8.6.2 Component: Compiler | Version: 8.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: #14677, #15155 | Differential Rev(s): Phab:D5196, Wiki Page: | Phab:D5201 -------------------------------------+------------------------------------- Comment (by osa1): Simon, you said that we can remove `can_fail=True` for `dataToTag#` after removing various hacks (in comment:60), and I also used to think that this should be the case, but thinking about this more I think `dataToTag#` should stay as `can_fail=True`. The reason is because `dataToTag#` evaluates the argument and returns an unboxed value, so I think these two expressions calls should have the same value: {{{ exprOkForSpeculation `dataToTag# foo` exprOkForSpeculation `case foo of x -> 1#` -- note: foo is lifted }}} Looking at the code I see that the latter returns `False` (because the scrutinee is lifted), so for the former to return false we need to mark `dataToTag#` as `can_fail = True`. Does this make sense? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15696#comment:68 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler